12 LIFE IN THE SEA [CH. 



Nothing in our ordinary experience gives us any 

 adequate idea of the physical conditions at the bottom 

 of the ocean. As we descend deeper and deeper the 

 temperature falls more and more, and at a depth 

 of about 400 fathoms the annual variations in the 

 temperature of the sea due to the seasons fade away, 

 and uniformity reigns. From about 400 fathoms 

 downwards the temperature would fall very slowly, 

 and everywhere in the North Atlantic it would not 

 be much higher than that of the freezing point of 

 fresh water. In the circumpolar seas it would fall 

 still further and in some places would be about two 

 degrees below zero of the Centigrade scale. 



The darkness would be greater than that of which 

 we have any ordinary experience. Even at a depth 

 of about ten fathoms the illumination would be that 

 of faint twilight only, and at fifty fathoms it would 

 be still less. The light there would be no longer 

 white, for sea water absorbs first the red, orange, 

 and yellow rays, and then the green, blue and violet. 

 At about 50 fathoms the violet light would still be 

 fairly strong, and it would be present even at a depth 

 of 200 fathoms, but there would be absolutely no 

 trace of the red rays. At about 400 to 500 fathoms 

 even the violet light would have disappeared entirely 

 and only the ultra-violet rays light which is invisible 

 to our eyes, would remain. At a depth of about 

 900 fathoms the last traces of ultra-violet radiation 



